1) Field of the Invention
The present invention relates to an image forming apparatus without a cleaning system, a process cartridge, a cleaning system, and an image forming apparatus that includes the cleaning system.
2) Description of the Related Art
An electrostatic transfer scheme is employed in some kinds of image forming apparatuses to transfer a toner image on a latent image carrier to a transferee. In the electrostatic transfer scheme, a transfer electric field is formed between the latent image carrier and the transferee that moves on a surface of the latent image carrier keeping a contact with the surface. In such apparatuses, a transfer residual toner remains on a portion of the surface of the latent image carrier after transferring the toner image. If the latent image carrier is used in a next image forming step with the transfer residual toner left unremoved on the portion, a charge failure, such as a nonuniform charge, occurs on that portion, causing image deterioration. Therefore, conventionally, a cleaning apparatus is provided at a position opposed to the surface of latent image carrier from a transfer area to a charging area to remove the transfer residual toner. Such a cleaning apparatus requires a space for installing a waste toner tank for storing the transfer residual toner collected from the surface of the latent image carrier, a recycle toner conveyor passage for conveying the transfer residual toner for recycling the collected transfer residual toner, and the like. This increases the size of the image forming apparatus.
To get around the problem of increasing the size of the apparatus, an image forming apparatus disclosed in Japanese Patent No. 3091323 (hereinafter, a patent document) has been devised, for example. This image forming apparatus adopts a scheme of collecting a transfer residual toner remaining on the surface of the latent image carrier by using a developing device (hereinafter, “developer collecting scheme”). In this developer collecting scheme, the developing device, which is provided for a purpose different from cleaning, is used for collecting a transfer residual toner. Therefore, no waste toner tank or recycle toner conveyer passage as described above is required to be separately provided. Thus, using such a developer collecting scheme can contribute to downsizing of the image forming apparatus.
Also, the patent document describes an example in which a charging device included in the image forming apparatus using the developer collecting scheme performs charging by making a charging roller in contact with the latent image carrier. Conventionally known schemes of uniformly charging the surface of the latent image carrier include a contact/proximity charging scheme in which the surface is uniformly charged by making a charging member, such as a charging roller, in contact with the surface, and a charger charging scheme for uniform charging with a corona charger. However, in the charger charging scheme, to cause the surface of the latent image carrier to have a desired potential, a large amount of discharge has to be generated. Therefore, a large amount of discharge products, such as ozone or nitrogen oxide, are generated, thereby causing a possible environmental problem. On the other hand, in the contact/proximity charging scheme, the amount of discharge is small compared with that in the charger charging scheme, and therefore this scheme is advantageous in view of environment. Therefore, according to the image forming apparatus disclosed in the example described above, the size of the apparatus can be made small, and also the amount of discharge products is small, thereby achieving a possible advantageous effect in view of environment.
However, in an image forming apparatus using both of the charger collecting scheme and the contact/proximity charging scheme, when the transfer residual toner on the latent image carrier is conveyed to a developing area, the transfer residual toner and the charging member may come in contact with or be proximity to each other. Therefore, the transfer residual toner may adhere to the charging member. The transfer residual toner adhering to the charging member may prevent uniform charging, thereby making it impossible to cause the surface potential of the latent image carrier at a desired potential and causing an insufficient charge, such as uneven charge. As a result, degradation in image density and background stain occur, thereby causing a problem of degradation in image quality. This problem does not restrictively occur when the developer collecting scheme is adopted, but also occurs as long as the apparatus has a structure in which a transfer residual toner is left unremoved from the latent image carrier and is conveyed to an area in contact with the charging member.
The Inventors have suggested the following apparatus (hereinafter, a first image forming apparatus) as an image forming apparatus that can solve the problem described above. In the first image forming apparatus, of the transfer residual toner remaining on the surface of the latent image carrier after transfer, a reversely-charged toner having a polarity reverse to a normally-charged toner charged with the same polarity as that of a charging bias is collected by a temporarily-retaining unit, such as a brush member, from the surface of the latent image carrier for retaining. As such, by collecting and retaining the reversely-charged toner, the reversely-charged toner can be prevented from adhering to the charging member. Then, the retained reversely-charged toner is returned to the surface of the latent image carrier at a predetermined timing, such as during a period starting from the completion of formation of an image until formation of the next image. Then, the reversely-charged toner returned on the surface of the latent image carrier is collected by a developing device or is transferred to a transferee or a conveying member for conveying the reversely-charged toner. According to the first image forming apparatus, while the returned reversely-charged toner is passing through the charged area, application of the charging bias is stopped or the charging member is separated from the latent image carrier. Therefore, the reversely-charged toner is prevented from adhering to the charging member.
The Inventors have also suggested the following apparatus (hereinafter, a second image forming apparatus) as an image forming apparatus that can solve the problem described above. In the second image forming apparatus, of the transfer residual toner remaining on the surface of the latent image carrier after transfer, a transfer residual toner having a polarity reverse to the polarity of a charging bias is collected and retained by a temporarily-retaining unit, such as a fur brush, from the surface of the latent image carrier for retaining. As such, by collecting and retaining the transfer residual toner having a polarity reverse to the polarity of the charging bias, the transfer residual toner can be prevented from adhering to the charging member. Then, the retained transfer residual toner having a polarity reverse to the polarity of the charging bias is returned to the surface of the latent image carrier at a predetermined timing, such as during a period starting from the completion of formation of an image until formation of the next image. Then, the transfer residual toner returned on the surface of the latent image carrier is collected by a developing device or is transferred to a transferee or a conveying member for conveying the transfer residual toner. According to the second image forming apparatus, while the returned toner is passing through the charged area, application of the charging bias is stopped or the charging member is separated from the latent image carrier. Therefore, the transfer residual toner having a polarity reverse to the polarity of the charging bias is prevented from adhering to the charging member.
However, in the first image forming apparatus, a normally-charged toner of the transfer residual toner is not collected by the temporarily-retaining unit, such as a brush member. Therefore, the normally-charged toner may pass through an area opposed to the latent image forming unit (hereinafter, a latent image forming area) during the step of forming of the next image to be collected by the developing device or be transferred to the transferee. Therefore, with the normally-charged toner adhering to the surface of the latent image carrier, a latent image is formed by the latent image forming unit on the surface of the latent image carrier. Thus, a portion where the toner adheres and a portion shadowed by the toner are not exposed, thereby posing a problem of occurrence of white dots on a solid image portion.
Similarly, in the second image forming apparatus, a toner having the same polarity as the polarity of the charging bias is not collected by the temporarily-retaining unit, such as a fur brush. Therefore, the uncollected toner may pass through the latent image forming area during the step of forming of the next image to be collected by the developing device or be transferred to the transferee. Therefore, with the transfer residual toner adhering to the surface of the latent image carrier, a latent image is formed by the latent image forming unit on the surface of the latent image carrier. Thus, a portion where the toner adheres and a portion shadowed by the toner are not exposed, thereby posing a problem of occurrence of white dots on a solid image portion.